Sources and sinks of bottom water oxygen in a seasonally hypoxic fjord

Deoxygenation of the ocean has been occurring over last half century, particularly in poorly ventilated coastal waters. In and estuarine environments, both water column sediments play key roles controlling oxygen variability. this study, we focus on controls concentration Bedford Basin (BB), a 70 m deep, seasonally hypoxic semi-enclosed fjord West Atlantic coast Nova Scotia. The basin is connected to Scotian Shelf via narrow 20 deep sill that restricts resupply bottom water. Hypoxia was recorded 2018, 2019 2021 with minimum 5, 6.7 2.7 μM, respectively. Using 1-D benthic-pelagic coupled model investigate consumption processes during these years. constrained weekly measurements temperature, salinity, chlorophyll-a fluorescence dissolved from monitoring station central together seasonal benthic diffusive uptake. Our suggested 29-81%, up 36% re-oxygenation occurred winter mixing period through summer/fall intrusions water, Occasional shelf rapidly, timescale few hours, delivered equivalent amounts as were sufficient end hypoxia. Collectively, mechanisms supplied majority Oxygen supply waters periods stratification accounted for 19-36% annual flux. mean uptake 12 ± 8 mmol -2 d -1 contributed ~20% total below depth. 2021, sea surface temperature (SST) unusually high likely resulted 50% less oxygenation compared 2018 due increased stratification; SST BB found be increasing at rate 0.11 0.02 °C/year. Climate control are discussed numerical experiments used compare effects different scenarios oxygenation.